The OP does not say that $scandir contains umlauts.

Neither my code nor the code the OP posted requires the utf8 pragma.

binmode(STDIN, ':encoding(UTF-8)');
chomp(my $scandir = <STDIN>);

#OR
$ perl -CS -e 'chomp(my $scandir = <STDIN>); ...'

#OR
$ perl -CA -e 'my $scandir = shift; ...' <dir>
[download]

I really don't think you understand what the utf8 pragma does. Here's another quote from the documentation (first line of the description):

"The use utf8 pragma tells the Perl parser to allow UTF-8 in the program text in the current lexical scope ..."

It has nothing to do with the:

• flagging variables ("getting $scandir flagged as UTF-8")
• encoding of STDIN, STDOUT or STDERR ("perl -CS ...")
• encoding of @ARGV elements ("perl -CA ...")

Let me reiterate the quote I provided in my earlier post from the utf8 documentation:

"Do not use this pragma for anything else than telling Perl that your script is written in UTF-8."

It has nothing to do with data read into the script, data processed by the script, data generated by the script or data output by the script. It's only about the text used to write the script and how Perl should parse that source text.

-- Ken

It has nothing to do with the: encoding of STDIN ... encoding of @ARGV elements

Correct.

It's only about the text used to write the script and how Perl should parse that source text.

Yes, so...

use utf8;

my $scandir = 'something with umlauts it it';
#              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
# ...is this string literal not part of the source?
[download]

It has nothing to do with flagging variables

#!/usr/bin/perl

use strict;
use Devel::Peek;

{
    use utf8;
    my $var = 'für';
    print Dump \$var;
}

my $var = 'für';
print Dump \$var;